Named parameters

Named parameters
You are encouraged to solve this task according to the task description, using any language you may know.

Create a function which takes in a number of arguments which are specified by name rather than (necessarily) position, and show how to call the function. If the language supports reordering the arguments or optionally omitting some of them, note this.

Note:

Named parameters relies on being able to use the names given to function parameters when the function is defined, when assigning arguments when the function is called.

For example, if a function were to be defined as define func1( paramname1, paramname2); then it could be called normally as func1(argument1, argument2) and in the called function paramname1 would be associated with argument1 and paramname2 with argument2.

func1must also be able to be called in a way that visually binds each parameter to its respective argument, irrespective of argument order, for example: func1(paramname2=argument2, paramname1=argument1) which explicitly makes the same parameter/argument bindings as before.

Named parameters are often a feature of languages used in safety critical areas such as Verilog and VHDL.

All callable entities (procedures, functions, entries) require named arguments. All of them can be called using either positional or keyed association of the actual arguments. The arguments supplied with default values can be omitted.

Function definitions in Applesoft BASIC using the DEF FN statement can only have one parameter. Subroutines and functions with many parameters can be simulated using global variables which are effectively named parameters. Default or optional parameters can be simulated with a check in the subroutine.

In Bracmat, all functions have exactly one argument, called "arg". To split the argument and assign values to local variables, you always have to use pattern matching.
In this task, the pattern is just made a bit more complex than would have been the case without explicit parameter names in the argument.

As a bonus, default values for the parameters left unspecified can be either implicitly set to zero by the struct initializer, or supplied in a wrapper-macro definition. But this is not idiomatic C by any stretch.

BOOST_PARAMETER_FUNCTION((int), // the return type of the function, the parentheses are required. function_with_named_parameters, // the name of the function. tag, // part of the deep magic. If you use BOOST_PARAMETER_NAME you need to put "tag" here.(required // names and types of all required parameters, parentheses are required.(foo, (int))(bar, (float)))(optional // names, types, and default values of all optional parameters.(baz, (bool) , false)(bonk, (std::string), "default value"))){if(baz &&(bar >1.0))return foo;return bonk.size();}

Once the definition is written, using it is easy, by name or position.

&key indicates that further parameters are named (keyword parameters); a bare symbol (e.g. first) has a default of NIL, whereas a list (e.g. (last "?")) gives the variable name and the default value (which is evaluated when the function is called, unlike Python).

In Common Lisp, the arguments to a function are always a simple list of values; the &key facility merely defines an interpretation of that list by the function: alternating keys and values. (As a result of this, mixing varargs (&rest) with named parameters is not recommended as it requires some additional means of distinguishing them. On the other hand, functions which pass their arguments on to other functions need not handle named arguments distinctly.)

Since E supports arbitrary pattern matching (in the sense of Pattern Matching in parameter lists, a map-pattern can be used to provide named parameters, though the syntax is sufficiently noisy that this is not used casually.

As with many of the other languages here, Forth does not have named parameters, but it does have practices that arise in situations where a Forth programmer might want named parameters. In Forth's case, these practices also arise when a more natural control language is wanted (e.g., LEFT ARM 36 DEGREES LIFT) or when a word would otherwise take excessively many arguments.

J is similar to Perl in that all arguments to functions come in as separate elements in an array. But it is possible to emulate more complex calling conventions. For example, using the calling convention J script, one could write:

With this version, ECMAScript adds destrucuring assignments and destructuring in function parameters. Thus you could do something like this (this works in ES6 Fiddle, but is syntax error in Mozilla SpiderMonkey JS Shell, so uses console.log instead of print):

let example =// The member name in the object can either be the same as the parameter (as in bar, grill),// or a different parameter name as in the case of member foo being assigned to parameter a here.({foo: a=0, bar=1, grill='pork chops'}={})=>( console.log('foo is ',a,', bar is ',bar,', and grill is '+grill));

Function calls in LabVIEW are implemented as instantiated VIs, small icons representing the function to be called. All parameters are positional, by drawing wires to different points along the icon edge. By right-clicking on the VI icon and unchecking "View as Icon", the parameter names can be shown. The parameter names are mainly informational for the user.

This image shows a VI with "View as Icon" unchecked.

This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

Lingo does not support named function parameters. But this can be simulated by using a single property list (hash) with named properties as function argument. You can also create functions that support both calling methods, like e.g. this function that accepts either 3 integers or a single property list with such named properties:

f := proc(a, {b:= 1, c:= 1}) print (a*(c+b));end proc:#a is a mandatory positional parameter, b and c are optional named parametersf(1);#you must have a value for a for the procedure to work 2f(1, c = 1, b = 2); 3f(2, b = 5, c = 3);#b and c can be put in any order 16

Foo(word = "Bird", number = 3) // an argument with a default value can be omitted from function callFoo(3, option = false, word = "Bird") // unnamed arguments must be in same order as function definition and precede named arguments

Objective-C, like Smalltalk, has a method call syntax that is visually identical to named arguments, but they are not optional and may not be reordered. (Optional arguments may be simulated by defining multiple methods with the same leading name part.)

Named arguments can be re-ordered, but two arguments of the same label cannot be re-ordered relative to each other.

Named arguments can be curried. If you partially apply a function on a named argument (even if the named argument is not first in the function declaration), it will evaluate to a function of the remaining arguments.

Named arguments can be made optional, with the ?(arg = value) syntax in the parameter declaration. See the optional parameters task for more details.

The procedure Foo is defined with pattern matching in the argument list. The ellipsis means that additional record fields are allowed. To access optional record fields, we have to explicitly try to select a field and provide a default value in case it is missing ("CondSelect").

Perl has no non-experimental formal parameters. Instead, Perl subroutines access all of their arguments through the special array @_. You can easily implement named arguments by making your function interpret @_ (or part of it) as a hash.

sub funkshun {my%h=@_;# Print every argument and its value.printqq(Argument "$_" has value "$h{$_}".\n)foreachsortkeys%h;# If a 'verbosity' argument was passed in, print its value# whatever that value may be.print"Verbosity specified as $h{verbosity}.\n"ifexists$h{verbosity};# Say that safe mode is on if 'safe' is set to a true value.# Otherwise, say that it's off.print"Safe mode ",($h{safe}?'on':'off'),".\n";}

The semantics of calling such a function follow directly from the semantics of using a hash. For instance, if you provide multiple values for the same named argument, only the last one will be used. An example call:

Phix supports named and optional parameters in a very simple, natural, and intuitive way, erring on the side of caution when faced with any potential ambiguity.
Optional parameters are specified simply by providing a default, any non-defaulted parameters must occur before (to the left of) any defaulted parameters.
Named parameters can be given (when invoking a routine) in any order, but must be grouped together after (to the right of) any non-named parameters.
Note that low-level builtins (those defined using AutoAsm() in psym.e/syminit()) do not support named parameters (maybe one day..), but everything else does.

Usually all parameters can be omitted. In the case of switch parameters this will cause them to assume the value false, for normal parameters they will have the value $null. This is not always the desired value, though. Default values can be given too:

function Greeting ($Name="Nobody"){Write-Host Hello,$Name!}

If the Name argument is omitted now, its value will be "Nobody" instead of $null:

A more detailed explanation of parameters, arguments, and how they are used is in the sections below. This is a simplified explanation:

In Python, a regular parameter of a function can be used as either a positional or a named parameter. The variable name that you use for the parameter when you declare the function becomes the "name" for the parameter, should you use it as a named parameter. When you call a function, you use the "name = value" syntax to provide the argument to a named parameter. The named arguments must come after all the positional arguments.

def subtract(x, y):return x - y

subtract(5,3)# used as positional parameters; evaluates to 2subtract(y =3, x =5)# used as named parameters; evaluates to 2

Parameters can be made optional by providing a default argument, as described in the optional parameters article.

The call of a function in python can use the following argument types:

Positional arguments that are mapped by their position in the call argument list to the defparameter name in the corresponding position of the function definition.

Sequence arguments that are the character "*" followed by an expression evaluating to a sequence (such as a list or tuple). The values from the sequence are unpacked and mapped like individual positional arguments to defparameters of the function definition. Sequence arguments are “evaluated before any keyword argument, irrespecctive of their relative positions in an argument list”.

All positional arguments must appear before any keyword argument.

Keyword arguments of the form parameter_name "=" value will map the value to the defparameter in the definition of the same name.

Mapping arguments that are the characters "**" followed by an expression evaluating to a mapping (such as a dict/hash). The key, value pairs from the mapping are unpacked and mapped like individual keyword arguments to defparameters of the function definition.

If the function definition includes a positional parameter, then if the assignment of positional arguments and sequence arguments in the call gives more values than the defparameters of the definition, then these extra arguments are assembled, in order, into a tuple that is assigned to the posparameter of the definition.

If the function definition includes a keyword parameter, then if the parameter name of any keyword arguments and mapping arguments in the call is unknown in the defparameters of the function definition, then these extra keyword/value pairs are assembled into a dict that is assigned to the keyparameter of the definition.

Any default parameter of the function definition that is not assigned a value at this point, but which has a default value, will be aassigned this default value, without re-evaluating the default value.

Any default parameter of the function definition that is still un-assigned will cause a TypeError exception to be raised.

In addition, multiple mappings to any parameter will raise a TypeError exception. (This includes multiple mappings into a keyparameter or keyword arguments clashing with positional/sequence arguments).

R parameters are all named; arguments can be passed either positionally or with explicit naming. The named arguments are matched to their parameters first, then the unnamed arguments fill in remaining slots. A parameter whose name begins with a period will not be matched to unnamed arguments. R allows abbreviated names to be used as long as they match uniquely to an argument.

/*REXX pgm shows named parameters when called as a subroutine/function*//*┌────────────────────────────────────────────────────────────────────┐ │ The syntax of: xxx = func1(parmName2=arg2, parmName1=arg1) │ │ │ │ in the REXX language is interpreted specifically as: │ │ │ │ xxx = func1( yyy , zzz ) │ │ │ │ where yyy is the logical result of comparing (the REXX variables)│ │ │ │ parmName2 with arg2 and │ │ │ │ where zzz is the logical result of comparing (the REXX variables)│ │ │ │ parmName1 with arg1 │ │ │ │ (either as two strings, or arithmetically if both "parmName2" and │ │ "arg2" are both valid REXX numbers. In the REXX language, there │ │ is no way to declare (define) what a variable is [or its type], as │ │ each literal that can be a variable is assumed to be one. If it's │ │ not defined, then its uppercase name is used for the value. │ │ │ │ Consider the one-line REXX program: say Where are you? │ │ causes REXX to consider that four-word expression as a "SAY" │ │ statement, followed by three REXX variables, each of which aren't │ │ defined (that is, have a value), so REXX uses a value which is the │ │ uppercased value of the REXX variable name, namely three values in │ │ this case, so the following is displayed: WHERE ARE YOU? │ │ │ │ [There is a mechanism in REXX to catch this behavior and raise the │ │ NOVALUE condition.] │ │ │ │ To allow a solution to be used for this task's requirement, and │ │ and not get tangled up with the legal REXX syntactical expressions │ │ shown, this REXX programming example uses a variation of the │ │ task's illustration to allow a method in REXX of using named │ │ parameters: xxx = func1('parmName2=' arg2, "parmName1=" arg1) │ │ │ │ Also, REXX allows the omitting of arguments by just specifying a │ │ comma (or nothing at all, in the case of a single argument): │ │ │ │ xxx = func1(,zzz) │ │ │ │ would indicate that the 1st argument has been omitted. │ │ │ │ xxx = func1(yyy) │ │ │ │ would indicate that the 2nd argument (and all other subsequent │ │ arguments) has/have been omitted. │ └────────────────────────────────────────────────────────────────────┘*/

parsearg count,itemX /*assume 2 values have been used,*//*or whatever ... just to show...*/do j=1forarg(); _=arg(1)/*now, lets examine each argument*/ifarg(j,'Omitted')theniterate/*skip examining if argJ omitted.*//*(above) This is superfluous, *//* but it demonstrates a method. */if\arg(j,"Exists")theniterate/*exactly the same as previous. *//*Only 1st char (2nd arg) is used*/ first=strip(word(_,1))/*extract the 1st word in arg(j).*/ifright(first,1)\=='='theniterate/*skip if 1st word isn't: xxx= */parsevar _ varname '= 'value/*parse the named variable &value*/if varname==''theniterate/*not the correct format, so skip*//*(above) fix this for real pgm. */callvalue varname,value/*use BIF to set REXX variable. */end/*j*/

Ruby 1.9 can fake the effect with a Hash. If a caller passes name: value pairs, Ruby makes a Hash, and the called method sees this Hash in its last argument. To complete the effect, the method may declare an optional last argument that defaults to an empty Hash {}. In this version, example(typo: 4) causes no error.

As for Objective-C the methods signature is made of "Symbol:[OtherSymbol:]*" (* stands for 0 or more repetition of the part in the brackets), without the possibility to reorder them (it would be another signature) or to make them optional.

Suneido can handle named and unnamed parameters. When using a combination, unnamed parameters must come before named ones and must be in the correct order. Named parameters can be in any order. Named parameters are given a default value so they are not mandatory.

Swift cannot handle named parameters in any order, but can handle named parameters in their defined order.
Whether or not you are required to specify named parameters is specified by the designer of that API.

Note that when you don't explicitly specify external parameter names, the behavior is different for functions, methods and initializers:

For a function or method, the first parameter doesn't have an external parameter name by default (as if you used _) unless you specify it; the rest of the parameters by default take the local parameter name as external parameter name if you don't specify one.

For an initializer, all parameters by default take the local parameter name as external parameter name if you don't specify one.

(Prior to Swift 2, for functions, all parameters by default don't have an external parameter name; it was changed to work the same way as methods in Swift 2.)

The simplest way of passing named parameters is to use the Tcl language's strong support for variadic commands together with its arrays. By convention (originally from Tk) the named parameters names start with a hyphen (“-”) and are called options.

proc example args {# Set the defaults array set opts {-foo 0 -bar 1 -grill "hamburger"}# Merge in the values from the caller array set opts $args# Use the argumentsreturn"foo is $opts(-foo), bar is $opts(-bar), and grill is $opts(-grill)"}# Note that -foo is omitted and -grill precedes -barexample -grill "lamb kebab" -bar 3.14# => ‘foo is 0, bar is 3.14, and grill is lamb kebab’

More complex option parsing is possible, e.g., with the opt package (of which only a small fraction of the functionality is shown here). This package also allows you to specify type constraints, though that is usually not necessary, and will generate a standard help message that can be obtained with the -help option:

package require opttcl::OptProc example {{-foo -int 0"The number of foos"}{-bar -float 1.0"How much bar-ness"}{-grill -any "hamburger""What to cook on the grill"}}{return"foo is $foo, bar is $bar, and grill is $grill"}example -grill "lamb kebab" -bar 3.14# => ‘foo is 0, bar is 3.14, and grill is lamb kebab’example -help# Usage information:# Var/FlagName Type Value Help# ------------ ---- ----- ----# ( -help gives this help )# -foo int (0) The number of foos# -bar float (1.0) How much bar-ness# -grill any (hamburger) What to cook on the grill

According to wiki.tcl.tk discussions, ::tcl::OptProc is deprecated.
The recommended replacement is cmdline in tcllib. "This is probably the most standard and widely-used of these packages."